Our TBRU focuses on immunity to M. tuberculosis (Mtb), to test the overall hypothesis that latent TB infection (LTBI) exists as a spectrum of bacterial and immunologic states, that at least three immunological states can be distinguished and correspond to: 1) past, but cleared Mtb infection; 2] stable LTBI with a low risk of progression to active disease; or 3) LTBI with a high risk of progression to active TB disease. To test this hypothesis, we will identify T cell signatures, consisting of the breadth of antigens recognized, the phenotypes, and the functions of Mtb-specific CD4 and CDB T cells, with correlations to outcomes determined in unique prospective studies in humans and in experimentally-infected nonhuman primates. In addition to unique prospective studies, we will use a novel 'Response Spectrum Assay' (RSA) that includes >60 strategically-selected Mtb antigens and epitope peptides, to assay the quantitative breadth and specific pattern of antigen recognition in LTBI subjects with distinct risks and rates of progreission to active TB. In addition, antigens and epitopes identified in the RSA will be used to design HLA-peptide tetramers for high-resolution studies of the phenotypes and functional capabilities of Mtb epitope-specific T cells. The results of these studies, which employ advanced technologies including mass cytometry (CyTOF), together with the results of the RSA, will be used to identify T cell signatures characteristic of distinct risk categories of LTBI. Certain of the validated T cell signatures will correspond to efficacious immune responses that are desirable targets of TB vaccine development, while others will be useful for identifying individuals with LTBI that are at highest risk of progression to active TB, so these individuals can be prioritized for preventive interventions. Our human studies will be conducted in Atlanta, GA, USA, and in collaboration with investigators at the Kenya Medical Research Institute/U.S. Centers for Disease Control (KEMRI/CDC); studies of TB in nonhuman primates will be done by experts at two national primate research centers (Yerkes and Tulane). The team we have assembled possesses a wide range of knowledge and expertise, and is poised to generate improved understanding of TB immunity to contribute to the elimination of TB.